1. Field of Invention
The invention relates to a variable valve mechanism of an internal combustion engine, and to an intake air amount control apparatus employing the variable valve mechanism.
2. Description of Related Art
Variable valve mechanisms for changing the operation angle and the valve lift of intake valves and exhaust valves in accordance with the state of operation of an internal combustion engine are known. Such variable valve mechanisms are disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2001-263015 (pages 9 and 10, and FIG. 21), and Japanese Patent Application Laid-Open Publication No. 5-18221 (page 4, and FIG. 2).
In a variable valve mechanism described in Japanese Patent Application Laid-Open Publication No. 2001-263015, the phase difference between an input portion and an output portion of an intervening actuation mechanism is changed by moving a control shaft in the direction of an axis, so as to adjust the starting position of valve lift caused by a cam.
In a variable valve mechanism described in Japanese Patent Application Laid-Open Publication No. 5-18221, a three-dimensional cam is moved in the direction along a shaft to change the cam profile in order to adjust the valve lift starting position.
The use of such variable valve mechanisms and three-dimensional cams for adjusting the amount of intake air supplied into an internal combustion engine instead of using, for example, a throttle valve or the like, has been considered. However, a possibility recognized in conjunction with the adjustment of the amount of intake air and the air intake timing based on the valve operation angle and the valve lift is that the adjustment via the variable valve mechanism may become less precise than the adjustment via a throttle valve depending on circumstances, and therefore may give rise to a problem in the operation control of the internal combustion engine.
The adjustment precision can be improve by, for example, reducing the rate of change of the valve operation angle or valve lift with respect to the amount of movement of the control shaft in the variable valve mechanism or reducing the rate of change of the valve operation angle or valve lift based on the change in profile of the three-dimensional cam in the direction of an axis of the cam. However, reduction of the aforementioned rate of change involves an increased range of movement of the control shaft, or a three-dimensional cam elongated in the direction of the axis. Thus, it becomes difficult to incorporate the variable valve mechanism into an internal combustion engine.
Another measure to improve the adjustment precision is adoption of a high-precision actuator for highly precise movement of the control shaft or the three-dimensional cam in the direction of the axis. However, the high-precision actuator is very likely to be large in size.